The sorption and crystallographic characteristics of alumina activated in a reactor for pneumatic transport

Abstract

Active transition alumina powders were obtained by flash calcination of gibbsite in a reactor for pneumatic transport in the dilute, two-phase flow regime in the temperature interval from 883 to 943 K with a residence time between 0.4 and 0.9 s. The results of X-ray diffraction analysis confirmed that the activated alumina samples were either microcrystalline or amorphous. From nitrogen adsorption-desorption isotherms, the specific surface areas of all samples were calculated by the BET method. Using the sorption data, the fractal dimension of the surface of the alumina samples was calculated according to a modified FHH method. By application of fractal geometry, using the values of the fractal dimension of the surface and of the specific surface area, the effective surface areas of the active aluminas were calculated for the adsorption of molecules having a cross-section area greater than that of the nitrogen molecule.

Kratkovremenom termičkom aktivacijom gibsita u reaktoru za pneumatski transport čestica na temperaturama u intervalu od 883 do 943 K i vremenu boravka od 0.4 do 0.9 s dobijen je aktivni prah aluminijumoksida. Rentgenska strukturna analiza pokazala je da dobijeni uzorci imaju visok stepen amorfnosti i mali procenat polaznog gibsita. Na svim uzorcima su određene adsorpciono - desorpcione izoterme azota iz kojih je po BET - metodi izračunata specifična površina. Na osnovu rezultata sorpciono - strukturne analize određene su fraktalne dimenzije površine FHH - metodom, koje su poslužile za sagledavanje efektivne površine uzoraka aktivirane alumine za adsorpciju molekula veće površine poprečnog preseka od molekula azota.